Coal-shale interface detection

ABSTRACT

A penetrometer for coal-shale interface detection for use with coal cutting equipment consisting of a reciprocating hammer having an accelerometer mounted thereon to measure the impact of the hammer as it penetrates the ceiling or floor surface of a mine. Additionally, a pair of reflectometers simultaneously view the same surface, and the outputs from the accelerometer and reflectometers are detected and jointly registered to determine when an interface between coal and shale is being cut through.

ORIGIN OF THE INVENTION

The invention described herein was made by employees of the UnitedStates Government, and may be manufactured and used by or for theGovernment of the United States for governmental purposes without thepayment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the art of detection of the interface betweencoal and shale, and particularly to a mechanized system of detection.

2. General Description of the Prior Art

As found, coal generally lies in seams of varying height with top andbottom interfaces with shale on top and clay on the bottom. In miningthe coal, it is thus important to be able to operate coal cuttingmachines so that cuts are made which just extend to, but not into, theshale; otherwise, all of the coal that could be mined will not be mined(if the cut falls short of the interface), or shale will be mined alongwith the coal (if the cut goes beyond the interface), and the quality ofthe coal will be adversely affected. For these reasons, it is highlydesirably that coal-shale interfaces be determined with considerableaccuracy. Up until now, the identification of floor-ceiling material hasbeen by the natural senses i.e.g, seeing, hearing and/or feeling, of aminer standing close to the cutting machine. Not only is this dangerous,but because of the severe environment, the sensitivity of one's naturalsenses of observation are not particularly keen or reliable.

Accordingly, it is the object of this invention to eliminate thenecessity of personal observation of ceiling and floor material of acoal shaft in the vicinity of a coal cutting machine and to accomplishidentification of the material by an electromechanical system which canperform the identification with improved accuracy.

SUMMARY OF THE INVENTION

In accordance with this invention, a penetrometer is constructed inwhich a ram is reciprocally driven. One end of the ram is hardened forstriking, without deformations, rock or shale. An accelerometer isattached to an opposite end region of the ram, and it provides anelectrical output in the form of a pulse which has distinctivecharacteristics enabling a "coal" signal to be distinguished from a"shale" signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial view of a penetrometer as contemplated by thisinvention.

FIG. 2 is a pictorial view illustrating the arrangement of apenetrometer and two reflectometers and a system for mounting thesedevices.

FIG. 3 is a graph illustrating the electrical response of thepenetrometer shown in FIG. 1.

FIG. 4 is an electrical block diagram of the system of this invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIG. 1, a ram or shaft 10 of penetrometer 12 is slidablysupported for reciprocal movement by bearing surface 14 of enclosure 16and bearing surface 18 of support plate 20, in turn supported byenclosure 16. Ram 10 is reciprocally driven through spring 24, aroundram 10, an end 26 of spring 24 being attached to supporting collar 27,in turn attached to ram 10. The opposite end, end 28 of spring 24, isattached to collar 30, slidably positioned around ram 10. Collar 30 isreciprocally driven through linked pivoted arms 32 and 34 of motor drive36. Motor drive 36 has a conventional motor drive through electricalleads 33 by a power source, which is not shown. Arm 32 is intermediatelypivoted by pin 38 on fixed support 40, and one end of arm 32 is drivenby motor drive 36 via longitudinal slot 44 in arm 32 and concentricallymounted pin 46 of motor drive 36. End 48 of arm 32 and end 50 of arm 34are pivotally interconnected by pin 52. Collar 30 has a flat cutoutregion 53 to accommodate the oscillation of arm 32 on collar 30. Thus,as pin 46 of motor drive 36 is rotated, as shown by arrow 54, collar 30is moved along ram 10 and imparts, through spring 24, reciprocalmovement of ram 10. As end 55 of ram 10 strikes a surface, spring 24compresses. Thus, there is avoided a positive, and perhaps destructive,force between motor drive 36 and ram 10. The impact on and penetrationinto the floor or ceiling material of a coal mine of ram 10 is sensed byaccelerometer 56 mounted on end region 58 of ram 10. Its electricaloutput is provided by leads 59 to the electrical circuitry illustratedin FIG. 4. FIG. 3 illustrates the response for the penetration of coaland shale. Thus, it will be noted that coal waveform 60 is of loweramplitude but has a wider base than shale waveform 62. Thesecharacteristics are employed, as will be further explained, todistinguish between coal and shale.

FIG. 2 illustrates housing 63 which encloses penetrometer 12 and themounting assembly by which housing 63 is supported by and operated as anaccessory of a coal cutting machine 64, such as, for example, a longwallshearer. Also, it illustrates a second feature of this invention, whichis the incorporation of two reflectometers, designated reflectometers 1and 2. The reflectometers are conventional, being basically lightresponsive switches which effect an electrical switching function when adiscrete level of light is reflected off of the surface of the minebeing examined. Each includes a light emitting diode which provideslight upward through windows 65 and a photodetector which senses thereflected light being passed back through windows 65. As shown,reflectometer 1 is positioned on one side of housing 63, andreflectometer 2 is positioned on an opposite side of housing 63, thusthere being one on each side of ram 10 of penetrometer 12. To facilitatemovement across the surface of a mine, the top or roof portion ofhousing 63 is tapered. The top or viewing surfaces of the reflectometersare sloped to eliminate debris from obscuring windows 65.

Penetrometer-reflectometer unit 66, as a whole, is mounted by virtue ofbase member 67 (by means not shown) on frame member 68 of coal cuttingmachine 64 (not shown in detail) by mounting assembly 69 which enablesvertical movement of the unit without change of orientation. Mountingassembly 69 is in the form of a parallelogram employing upper parallelarm bars 70 and 72 and lower parallel bars 74 and 76. The bars arerectangularly spaced, and each is connected at one end by a pin 78 tohousing 63. The opposite end of lower bars 74 and 76 are supported bypivot pins 79 through cross bar 80 on column 82, attached to base member67. Upper bars 70 and 72 are longer than lower bars and areintermediately attached by pivot pins 84 to cross member 86 on column82. As shown, the distance of all bars between housing 63 and cross barsare identical.

An additional function of mounting assembly 69 is to spring biaspenetrometer-reflectometer unit 66 against a surface of a mine (e.g., aroof), and this is effected by a lever formed of extensions 88 and 90 ofupper parallel bars 70 and 72 and spring bias assembly 92. The ends ofextensions 88 and 90 are connected by cross arm 94, and spring biasassembly 92 is coupled between cross arm 94 and base member 67. Springbias assembly 92 employs a tubular spring enclosure 95 which has a lowerhook 96 connected through opening 98 to gusset 100 on base member 67. Aspring 102 is coiled within tubular spring enclosure 95 and attached totubular spring enclosure 95 at an upper end 106. The lower end of spring102 is axially engaged by adjustment shaft 108, which shaft is threadedinto cross arm 94, as shown. Then, by rotation of handle 110 of shaft108, the levered position of mounting assembly 69 may be varied andtypically would be adjusted to effect a light but constant engagementbetween penetrometer-reflectometer unit 66 and the surface of a mine. Inorder to provide a limited, rotation of column l82, and thereby afollowing movement by penetrometer-reflectometer unit 66, column 82 isrotatable on base member 68, but is limited by column mounted stops 112and gusset 100.

Referring to FIG. 4, the electrical output of penetrometer 12, obtainedfrom accelerometer 56, is amplified by amplifier 114, and in oneinstance the amplified signal provided to threshold detector 116. Atypical response of the output of amplifier 114 is illustrated in FIG. 3wherein waveform 60 is illustrative of a signal from the impact of ram10 on coal, and waveform 62 is illustrative of a signal from the impactof ram 10 on shale. Threshold detector 116 is simply an operationalamplifier wherein the signal input is applied to one input terminal, andan adjustable bias is applied to the other input terminal; and thus byadjustment of bias, the amplifier will provide one output state untilthe input signal reaches a selected level and then provide anotherstate. In this case, the selected level is chosen, for purposes ofillustration only, at 6 volts, and this will correspond to a signallevel as shown in FIG. 3 just above the anticipated maximum signal frompenetrometer 12 when impacted against coal.

The output of threshold detector 116 is fed to retriggerable one-shot118 which is retriggered at the rate of impact penetrometer 12. One-shot118 is triggered on by an output of threshold detector 116, indicatingthe presence of a signal responsive to the impacting of penetrometer 12on shale. So long as a shale indicating signal is applied to one-shot118 before it normally rests, there will remain, constantly, as anoutput of one-shot 118, a "low" or 0 state which is applied as one inputto two-input AND gate 122. Thus, with this posture, AND gate 122 is notenabled by this signal. However, when the input signal at thresholddetector 116 is below 6 volts, the retriggerable one-shot will not beretriggered on; and its output will be at a "high" or true state, whichwill enable AND gate 122 to pass a "coal" signal if coal is otherwiseidentified by the circuitry.

To further identify coal, a second output of amplifier 114 is applied tothreshold detector 124, a 1-volt threshold detector, it being adapted toprovide a "high" or true output state when the input signal exceeds the1-volt level. The 1-volt level of the threshold signal is chosen as alevel which is above normal noise conditions. For purposes of circuitcompatibility with the circuitry to follow, the output of thresholddetector 124 is inverted by inverter 126, and the signals that followhave na opposite polarity to those shown in FIG. 3.

Significantly, at the 1-volt level (with the present circuitry), and asshown in FIG. 3, the signal width or duration is greater for coal(waveform 60) then for shale (waveform 62). Thus, the duration of a coalderived signal is indicated as 464 microseconds, and a coal derivedsignal is indicated as 367 microseconds. Accordingly, a dividing linefor comparison has been set at 450 microseconds, and one-shot 128includes time constant circuitry to cause it to remain in an "on" statefor 450 microseconds after it has been triggered, it being triggered bya negative going, leading, edge of the pulse signal output of inverter126. The output of one-shot 128 is applied as a 450-microseconddisabling input to one-shot 130. Additionally, the pulse output signalof inverter 126 is applied to one-shot 130 which is triggered by thepositive, trailing, edge of the pulse signal in the absence of thedisabling 450-microsecond signal. Accordingly, if the trailing edge ofthe pulse signal arrives more than 450 microseconds after the leadingedge, which would be the case for a coal signal, one-shot 130 istriggered to provide a "true" input to AND gate 122. Then, assuming thatthreshold detector 116 acknowledged that the amplitude of a signal isnot greater than 6 volts, and thus retriggerable one-shot 118 is nottriggered, both inputs to AND gate 122 will be "true"; and a "true" or"coal" indicating signal will be supplied as a "coal" signal to terminal32 of selector switch 134.

In the event that either threshold detector 116 had indicated a level inexcess of 6 volts, or the duration of the signal had been less than 450microseconds, the output of AND gate 122 would not have become "true",and there would have been indicated on terminal 120 a 0 or "shale"signal.

Reflectometers 1 and 2 also provide an indication of the presence ofcoal or shale, and operate by virtue of the observation that thereflected light from shale is about three times greater than that fromcoal. The reflectometers are identical, and as stated above, eachcomprises a light responsive switch. In order to provide a "high" or"true" output responsive to the presence of coal in keeping with theoutput of the penetrometer portion of the circuitry, switching means areincluded in each penetrometer to connect to its output a "high" or"true" output for conditions of low light states. With a high lightstate, the reflectometers are adapted (as by opening a bias circuit) toprovide a 0 output, indicative of shale.

The output of reflectometer 1 is connected to terminal 136 of selectorswitch 134, and the output of reflectometer 2 is connected to terminal138 of this switch. Thus, there would be present on switch terminals132, 136, and 138 separate coal-shale indicating signals derived,respectively, from penetrometer 12, reflectometer 1, and reflectometer2. To further improve the accuracy capability of the system, these threesignals are supplied to a voting circuit which provides as an output asignal representative of the majority signal state. Accordingly, eachsignal is applied to an input of each of two of three AND gates of thecircuit. Thus, the penetrometer signal from terminal 132 is connected toan input of AND gates 140 and 142, the reflectometer 1 signal fromterminal 136 is connected as an input to AND gates 140 and 144, and thereflectometer 2 signal from terminal 138 is connected as an input to ANDgates 144 and 142. The outputs of the AND gates are connected as inputsto OR gate 146, and its output is connected to terminal 148 of selectorswitch 134, at which terminal a signal representative of the majoritysignal would appear.

To further examine the voting circuit, and with the selector switchoperated as shown to provide a voted output on terminal 148, it is to benoted that each of the three significant coal-shale signals appear atterminals 132, 136, and 138 and are "high" or true when coal isdetected, and "low" or 0 when shale is detected. Thus, with an outputfrom each terminal being connected to an input to two of the three ANDgates 140, 142 and 144, it is clear that when there occurs a "high" or"coal" indicated output on at least two of the terminals, at least oneof these AND gates will be made "true" and provide an output to OR gate146. When this occurs, OR gate 146 will provide a "true" output throughterminals 148 and 150 of selector switch 134 to coal indicator light 152to cause it to be illuminated. On the other hand, in the event that onlyone of the detection signals is "true", or none of them are "true", thenall of the outputs of AND gates 140, 142 and 144 will be false, andthere will be a "0" output of OR gate 146, which when inverted byinverter 154, will provide a "true" or high input to shale indicatorlight 156, causing it to be turned on. Of course, with a 0 outputapplied to coal indicator light 152, it would not be illuminated. WhileAND and OR gates are employed in the illustrated circuitry as logicelements, the more common NAND gate may be employed in their stead.

If selector switch 134 is operated to provide, as it may be, an outputfrom a single detection device, only that signal will be effective inproviding a coal or shale signal from selector switch 134, and theindication circuit will be operated as described, but responsive only toa single detection signal.

From the foregoing, it will be appreciated that this invention providesa practical electro-mechanical system for accurately distinguishingbetween shale and coal surfaces in a mine without the need of a humanobserver. Further, it provides for separate and combined utilization oftwo forms of detection apparatus to enable improved accuracy over widelyvarying conditions.

Having thus described our invention, what is claimed is:
 1. Apenetrometer for coal-shale interface detection comprising:an elongatedram; a frame and bearing means supported by said frame for engaging andslidably constraining said ram for movement parallel to the longitudinaldimension of said ram; a hard surfaced end on one end of said ram; drivemeans for repeatedly reciprocally moving said ram along a line parallelto the longitudinal dimension of said ram wherein said drive meansincludes linear force means and spring means coupled between said linearforce means and said ram for applying movement to said ram, and whereinsaid linear force means comprises:a. a motor and an eccentric memberdriven by said motor; b. a lever arm and pivot for intermediatelypivoting said lever arm; c. one end region of said lever arm beingslidably coupled to said eccentric, whereby said lever arm is oscillatedabout said pivot; d. coupling means for coupling an opposite end regionof said lever arm to said spring; and accelerometer means coupled tosaid ram for providing an electrical output representative of the rateof change of velocity of said ram responsive to said hard surfaced endof said ram striking a material, and thereby provide a signal indicativeof the presence of coal, and, alternatively, shale.
 2. A penetrometer asset forth in claim 1 wherein said coupling means comprises:a collarpositioned around and slidably mounted on said ram; pivot means forconnecting said opposite end of said lever arm to said collar; and saidspring being connected between said collar and said ram.